Hollow conduit and a method of making the same



Feb. 12, 1946. J. A. STADTFELD I 2,394,818 I HOLLOW CONDUIT AND A METHOD OF MAKING THE SAME Filed April 14, 1942 IN VEN TOR, JACOB A. STADTFELD.

ATTORNEY.

Patented Feb. 12 1946 HOLLOW CONDUIT AND A METHOD OF MAKING THE SAME Jacob A. Stadtfeld, San Francisco, Calif.,,assignor to Harry A. Button, Jr., San Francisco,

Calif.

Application April 14, 1942, Serial No. 438,882

2 Claims. (01. 138----76) The present invention relates to improvements I in hollow conduits and a method of making the same and has particular reference to stove pipes, furnace pipes and the like, which are usually made of rather large diameter and of light-weight material and the principal functions of which are to conduct gases in the absence of any considerable pressure, such as heated air or products of combustion.

Conduits of this type at the present time are usually made of relatively light sheet metal which is often covered with flexible sheets of asbestos for insulation purposes.

In the present emergency sheet metal isdifiicult to obtain and it is the principal object of the present invention to make asbestos available for the manufacture of pipes of this character.

Asbestos is available on the open market in the form of asbestos millboard, that is, in the form of relatively stiff sheets resembling ply-wood in their resistance to bending stresses, and normally not adapted for bending into tubular form without wrinkling on their inner faces and rupturing on their outer faces. 7

I have found, however, that if such asbestos millboard is subjected to a more or less conven-' tional rolling process, whereby it is turned uniformly throughout its length and to a relatively large diameter it is adapted to be shaped permanently into annular form, without any injury to the inner and outer surfaces thereof.

I have further found that the material when thus rolled into annular form, has a certain resiliency and elasticity so that when it is turned to a diameter slightly less than the desired'diameter and is expanded to the desired diameter thereafter it will tend to contract and cause confronting edges thereof to bear upon one another with a certain amount of pressure which facilitates the joining of the said edges.

When tubes of this character are provided with a suitable coating of hardening material for filling the pores on the inside and on the outside, they assume an almost metallic character and are not only impervious to gases but form excellent insulators and are exceedingly well adapted. to take the place of metallic conduits heretofore employed.

Conduits of this type may also be made in rectangular form, in which case the rolling action is, of course, omitted and the millboard is used in its original form.

It is the principal object of the present invention to provide conduits made of asbestos mill- 55 proportions of one-half a gallon of silicate of board and to provide a method of making the same. I v

Further objects and advantages of my invention will appear as the specification proceeds.

The preferred forms of my invention are illustrated in the accompanying drawing in which Figure 1 shows a method of making a circular conduit of asbestos millboard; I

Figure 2, a section isometric view of a finishe tube section;

Figure 3, a longitudinal section through a joint between two adjacent conduit sections;

Figure 4, an end view of a rectangular conduit section made in accordance with my invention, a blank for making the same being shown in dotted lines; and

Figure 5, a longitudinal section through a joint between two adjacent rectangular pipe sections.

WhileI have shown only the preferred forms of my invention, it should be understood that various changes and modifications may be made within the scope of the claims attached hereto without departing from the spirit of the invention.

Referring to the drawing in detail, a sheet I of asbestos millboard is fed, by anysuitable machinery, not illustrated, between two feed rollers 2 and 3 against a third roller 4 which bends the sheet into cylindrical form, preferably on a diameter slightly smaller than the diameter desired for the completed conduit so that when the rolling action is completed, the sheet of asbestos millboard assumes the substantially cylindrical form shown as the second step in Figure l, with the edges 5 and 6 overlapping.

A strip 1, preferably made of the same material, is then attached by any suitable means, such as stapling indicated at 8, to one of the overlapping edges, in such a manner that a section of the strip projects beyond the edge. Next the conduit is expanded, and upon release the edge 6 is made to seat upon the projecting portion of the strip 1, which forms a ledge, and the resiliency of the material will tend to urge the edge 6 upon the ledge and into contact with the edge 5. The edge 6 may then be secured upon the ledge by any suitable means. as by the staples 9 shown in Figure 2. A suitable anvil or mandrel l0 maybe used to facilitate this operation.

The entire section is now dipped into a suitable tank containing a hardening solution. This solution may be of any desired composition, depending upon the character of coating desired. My preferred solution comprises a mixture in the soda, one-half .a gallon of water and one pound of china clay. The tube section is allowed to remain in this solution for about four minutes, is then removed, drained and dried at about 200 degrees Fahrenheit for a period of four hours.

For joining two sections I preferably use a collar I I which may be similarly prepared and coated, 01' which may be made; in laminations as indi-i cated in' Figure 3. The collar is provided with an annular groove I2 forming a bead I3 on the. inside of the collar. Two pipe sections I are telescoped into the collar from opposite. ends as;

shown in Figure 3 to abut against the bead; and the groove l2. maybe used to a commodate a supporting wire, not shown, if the conduit is to be supported from a ceiling or the like; as is the usual practice, where the conduit is used as a furnace pipe in a basement. 7

In the form shown in Figures '4 and 5 con.-

duit I5 is. rectangular in form and is preferably made out of a blank shown in, dotted lines; This blank comprises four flat sections of asbestos millboard, indicated at. 1.6, I'I, I-8 and I9- respectively, alternating. sections IE.I 8- and I- l-.-I9-' being of similar dimensions. The blank is adapted for spreading onv a: flat: surface, which form V is, particularly adapted for; stacking and ship-v opposing sections are p-rovidedw'rth foreshortened reinforcing sheets 21. which. serve as. abuttments for: the othertwo sectionswhen the four sections are assembled in rectangular; formas. shown in Fi ure 4. The two free. edges are joined. in a I 7 similar manner by a suitable tape.

To. assemble froma blank; the. latter is spread ona flat. surface as shown. dottedglines in Ei ure 4.; Thesection I6;is then swung upward.

with its lower edge bearing against the edge of section I! and the reinforcing sheet 2| bearing on the top surface of section I I. Next the section I8 is swung upward in a imilar manner and the 5 section I 9 is swung into position to form the top. When the pipe is thus assembled, the two side sections I6 and I8 bear against the end edges of sections} I1 and I9; and the top and :bottom sec tions IT and I9 bear against the abutments 2I. The binders or tapes 20 hold the difierent sections in assembled relation.

The entire pipe section is now dipped, drained dried in the manner previously described.

For joining two sections of the rectangular type I preferably use a rectangular collar 22, which may be made in a. similar manner. The two sections I5 are telescoped on the collar to come up against an annular bead 23 formed by grooving the asbestos material.

The coating hardens the surface of s, sea-1st e p e es ins uble when drie prevents the softening and distorting oi the bestos in the presence of oisture; improves the; insulating characteristics of thei asbe tos and is. highly heat-resistant.

r h c s used. r joining the pipe sections may be ade of: n e aminations draw-n through a bath for applying the solution andmay;

be readily grooved while still Wet,

uardagainst sagins. o the wider; walls o th r c angular tube a l n itudinal. vane or p i n 25 may e sed: t enter of: the. collar 22. 1

I- claim:

to form an annular hollow conduit and-tonsione .to have opposing edges bearupon one. another under pressure, a strip of the same material-cisposed adjacent to said opposingedges, and'rneans 0 for securing the latter-upon the strip.

2. A plain. strip of asbestos millboard shapedto form anan-nular hollow conduit. andtensionedthe asbes- V 1. A plain s eet or asbestosmi-llboard: shaped. 

